Cis,endo-2-azabicycloalkane-3-carboxylic acid derivatives, their use and intermediates in their preparation

ABSTRACT

The invention relates to compounds of the formula I ##STR1## in which n is 1, 2 or 3, 
     Z 1  and Z 2 , and Z 3  and Z 4 , in each case together represent a chemical bond or 
     Z 1 , Z 2 , Z 3  and Z 4  in each case represent hydrogen, 
     Z 1  and Z 2  being in the cis configuration relative to one another and the COR 1  group on C atom 3 being in the endo configuration relative to the bicyclic ring system, 
     R 1  denotes hydroxyl, alkoxy, aralkoxy, amino, alkylamino or dialkylamino and 
     R 2  denotes hydrogen, alkyl, aryl, aralkyl, cycloalkyl or alkylcycloalkyl, 
     processes for their preparation and their use.

This application is a continuation of application Ser. No. 769,356, filed Aug. 26, 1985 now abandoned.

The invention relates to compounds of the formula I ##STR2## in which

n is 1, 2 or 3 and

(a)

Z¹ and Z², and Z³ and Z⁴, in each case together represent a chemical bond,

R¹ denotes hydroxyl, (C₁ -C₆)-alkoxy, (C₆ -C₁₂)-aryl-(C₁ -C₄)-alkoxy, amino, (C₁ -C₆)-alkylamino or di-(C₁ -C₆)-alkylamino and

R² denotes hydrogen, (C₁ -C₈)-alkyl, (C₆ -C₁₂)-aryl, (C₆ -C₁₂)-aryl-(C₁ -C₆)-alkyl, (C₃ -C₈)-cycloalkyl or (C₇ -C₁₂)-alkylcycloalkyl, or

(b)

Z¹, Z², Z³ and Z⁴ in each case represent hydrogen, Z¹ and Z² being in the cis configuration relative to one another and the COR¹ group on C atom 3 being in the endo configuration relative to the bicyclic ring system,

R¹ denotes hydroxyl, (C₁ -C₆)-alkoxy, (C₆ -C₁₂)-aryl-(C₁ -C₄)-alkoxy, amino, (C₁ -C₆)-alkylamino or di-(C₁ -C₆)-alkylamino and

R² denotes (C₁ -C₈)-alkyl, (C₆ -C₁₂)-aryl, (C₆ -C₁₂)-aryl-(C₁ -C₆)-alkyl, (C₃ -C₈)-cycloalkyl or (C₇ -C₁₂)-alkylcycloalkyl,

with the exception of those compounds of the formula I, known from J. prakt. Chem. 314 [1972] 353, 354, in which Z¹ -Z⁴ are defined as under (a), n=1, 2 or 3, R¹ denotes ethoxy and R² denotes methyl.

Alkyl (as such or as a constituent of other radicals) can be straight-chain or branched. Aryl is understood here, and in the following text, as meaning preferably phenyl, naphthyl or biphenylyl, especially phenyl.

European Patent Document No. A-79022 has disclosed compounds of the formula IV and its mirror image ##STR3## in which the hydrogens on the bridgehead C atoms are in the cis configuration relative to one another and the carboxyl group on C atom 3 is in the endo configuration relative to the bicyclo ring system, as well as a process for their preparation by reaction of an enamine of cyclopentanone with a compound of the formula V ##STR4## in which R denotes alkyl or aralkyl, Y denotes a nucleus-repelling group and Z denotes alkanoykl, aroyl or another protecting group conventionally used in peptide chemistry, cyclization of the resulting compounds of the formula VI ##STR5## to give compounds of the formula VIIa or VIIb ##STR6## and subsequent hydrogenation of these compounds (see reaction scheme I). ##STR7##

If commercially available starting materials are used (cyclopentanone and D,L-serine methyl ester hydrochloride), the compound of the formula IV+mirror image are obtained in a 7-step synthesis. As the compounds of the formula IV are intermediates in the preparation of highly active angiotensin-converting enzyme inhibitors, as disclosed in European Patent Document No. A-79022, it is of great interest to prepare compounds of the formula IV of related compounds in a particularly economic manner, i.e. using inexpensive starting materials, in the smallest possible number of reaction steps.

The compounds of the formula I according to the invention are easily obtainable intermediates in the preparation of highly active angiotensin-converting enzyme inhibitors.

Preferred compounds of the formula I are those in which

R¹ denotes hydroxyl or (C₁ -C₆)-alkoxy and

R² denotes hydrogen or (C₆ -C₁₂)-aryl-(C₁ -C₆)-alkyl, particular preference being given to those (C₆ -C₁₂)-aryl-(C₁ -C₆)-alkyl radicals which can be removed by catalytic hydrogenation, such as, for example, benzyl, p-nitrobenzyl, p-methoxybenzyl, α-phenylethyl or benzhydryl.

Compounds of the formula I in which Z¹ -Z⁴ are defined as above under (a) have 2 double bonds (see formula VIII). ##STR8## Compounds of the formula I in which Z¹ -Z⁴ are defined as above under (b) possess two hydrogen atoms, on bridgehead atoms 1 and 5, which are in the cis configuration relative to one another and the CO--R¹ group is in the endo configuration relative to the bicyclic ring system. The carbon atom in the 3-position has the R configuration (formula IX) or S configuration (formula X). The present invention includes optically pure compounds of the formulae IX and X as well as a mixture thereof. ##STR9## The S configuration in the 3-position is preferred.

Preference is also given to compounds of the formula I in which n=1, especially those compounds of the formula VIII in which R¹ denotes ethoxy and R² denotes benzyl.

The invention further relates to a process for the preparation of a compound of the formula I in which n is 1, 2 or 3,

Z¹, Z², Z³ and Z⁴ in each case represent hydrogen,

Z¹ and Z² being in the cis configuration relative to one another and the COR¹ group on C atom 3 being in the endo configuration relative to the bicyclic ring system,

R¹ denotes hydroxyl, (C₁ -C₆)-alkoxy, (C₆ -C₁₂)-aryl-(C₁ -C₄)-alkoxy, amino, (C₁ -C₆)-alkylamino or di-(C₁ -C₆)-alkylamino and

R² denotes hydrogen, (C₁ -C₈)-alkyl, (C₆ -C₁₂)-aryl, (C₆ -C₁₂)-aryl-(C₁ -C₆)-alkyl, (C₃ -C₈)-cycloalkyl or (C₇ -C₁₂)-alkylcycloalkyl, wherein a compound of the formula I in which

Z¹ and Z², and Z³ and Z⁴, in each case together represent a chemical bond and

n, R¹ and R² are defined as above is catalytically hydrogenated, and also to process for the preparation of a compound of the formula I in which Z¹, Z², Z³, Z⁴, R¹ and R² are defined as set at the outset under (a) and n has the above meanings, wherein a glycine derivative of the formula II

    R.sup.2 --NH--CH.sub.2 --CO--R.sup.1                       (II)

in which R¹ and R² are defined as above, is reacted with a compound of the formula III ##STR10## in which n is 1, 2 or 3 and Hal represents halogen, preferably chlorine.

Radicals R¹ ≠hydroxyl can be cleaved to form R¹ =hydroxyl, if appropriate with the aid of an acid or a base. Preferred acids are mineral acids such as H₂ SO₄ or HCl. Preferred bases are alkali metal hydroxides such as NaOH or KOH.

It is preferred to prepare a compound of the formula VIII in which n=1, R¹ denotes ethoxy and R² denotes benzyl. By catalytic hydrogenation with cleavage of the benzyl group, this compound can then be converted to a compound of the formula IX or X in which n=1, R¹ denotes ethoxy and R² denotes hydrogen.

The processes according to the invention have made it possible to reduce the number of reaction steps to four, with good yields, using inexpensive, commercially available starting materials (for example cyclopentanone and N-benzylglycine ethyl ester).

A preferred embodiment is shown in reaction scheme II (R¹ =OH, R² =H, n=1, 2, 3). ##STR11##

If glycine derivatives of the formula (II) in which R¹ and R² have the meanings given above are used in the 2nd reaction step, compounds of the formula VIII are obtained which are catalytically hydrogenated to give compounds of the formula IX and its mirror image X.

In a preferred process according to the invention, the compounds of the formula XI in which n=1, 2 or 3, known from the literature (Chem. Ber., 2743 (1960)), which are very readily obtainable in very good yield, are reacted with glycine derivatives of the formula II. The reaction is particularly preferably carried out with N-benzylglycine ethyl ester. The reaction can be carried out without a solvent in such a way that equivalent quantities of the compounds of the formulae II and XI are reacted in the presence of an organic base such as, for example, triethylamine, diisopropylethylamine, dicyclohexylethylamine, N-ethylmorpholine etc., in a temperature range between 0° C. and 160° C., preferably between 20° C. and 120° C. The base can be used in an equimolar proportion, in excess or in a quantity less than the stoichiometric proportion. The organic base can also be replaced by a corresponding excess of the compound II. The reaction described above is carried out without a solvent or in a polar or non-polar organic solvent, in a temperature range between 0° C. and the boiling point of the solvent. Toluene or benzene have proved particularly advantageous. At reflux temperature, the water of reaction formed can be entrained with these solvents. The water of reaction can also be removed with other water-binding agents such as, for example, MgSO₄, a molecular sieve, etc. The reaction mixture is extracted with a non-polar aprotic solvent such as, for example, hexane, petroleum ether etc., if appropriate after evaporation of the reaction solvents, the pyrrole derivative already being obtained in a relatively pure state. It can be used in this state of purity in the following reaction. If further purification is necessary, it can be filtered on silica gel or aluminum oxide with an organic solvent. The pyrrole derivative of the formula VIII is catalytically hydrogenated in an organic solvent, preferably in an alcohol such as, for example, ethanol or methanol, to give the compounds of the geneal formula IX and its mirror image X. The hydrogenation can be carried out at room temperature or an elevated temperature of up to 100° C., under normal conditions or under pressure. A temperature of between 20° and 60° C. and a pressure of between 1 and 100 bar are preferred. Suitable catalysts are Raney nickel or noble metal catalysts such as, for example, palladium, platinum or rhodium. Palladium-on-characoal has proved particularly advantageous. The hydrogenation can be carried out in the presence of an inorganic or organic acid. The addition of sulfuric acid has been shown to be particularly advantageous. If compounds of the formula VIII in which R² is a radical which can be removed by hydrogenation, such as benzyl, are used in the hydrogenation reaction, compounds of the general formula I in which R² =hydrogen are formed.

In the processes according to the invention, particular emphasis is to be placed on the selectivity of the hydrogenation reaction, which gives the cis,endo product diastereoselectively under the conditions indicated above.

The examples which follow are intended to illustrate the invention without thereby limiting it.

EXAMPLE 1 Ethyl 1-benzyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole-2-carboxylate

46.7 g (0.358 mol) of 2-chloro-1-formylcyclopent-1-ene are dissolved in 400 ml of toluene. 138 g (0.716 mol) of N-benzylglycine ethyl ester are added. The mixture is refluxed for one hour, the water of reaction being separated off via a water separator. After cooling, any precipitate formed is filtered off with suction and the toluene solution is washed with water, dried and concentrated. The residue is taken up in 300 ml of ethanol, 600 ml of 2N hydrochloric acid are added and the mixture is extracted 3× with petroleum ether. The petroleum ether phase is washed with 2×175 ml of ethanol/2N hydrochloric acid 1:2 and then with 100 ml of saturated NaHCO₃ solution, the organic phase is dried over MgSO₄, stirred with active charcoal and filtered with suction, and the filtrate is evaporated in vacuo. Yield: 53.1 g of oil.

¹ H-NMR (CDCl₃, 60 MHz):=1.26 (t; CH₃), 2.2-2.8 (m, 6H, 3CH₂), 4.18 (q; O--CH₂), 5.48 (s; N--CH₂), 6.78 (s; pyrrole-H), 6.9-7.5 (m; C₆ H₅).

EXAMPLE 2 Ethyl 1-benzyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole-2-carboxylate

25 g (0.191 mol) of 2-chloro-1-formylcyclopent-1-ene are added to 73.9 g (0.382 mol) of N-benzylglycine ethyl ester at room temperature and the mixture is then heated to 110° C. Working-up is carried out as indicated in Example 1.

EXAMPLE 3 Ethyl cis,endo-2-azabicyclo[3,3,0]octane-3-carboxylate

53.1 g of ethyl 1-benzyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole-2-carboxylate are dissolved in 450 ml of ethanol, and 5 g of Pd/C (10%) and 10.5 ml (19.3 g) of concentrated sulfuric acid are added to this solution. The mixture is then hydrogenated for 24 hours at 30° C. and under a hydrogen pressure of 100 bar. After the catalyst has been filtered off with suction, the solution is concentrated to half its volume in vacuo and adjusted to pH 7 with 2N sodium hydroxide solution. After concentration on a Rotavapor®, the residue is taken up in 2N hydrochloric acid and the aqueous solution is washed with ethylene chloride. This solution is then rendered basic with K₂ CO₃, saturated with NaCl and extracted with methylene chloride. After drying over MgSO₄ and treatment with active charcoal, the extract is concentrated in vacuo.

Yield: 28 g.

¹ H-NMR (CDCl₃, 270 MHz): 1.25 (t; 3H), 1.32-1.70 (m; 7H), 1.32 (broad s; NH), 2.27-2.39 (m; 1H), 2.50-2.66 (m; 1H), 3.59 (dd, J₁ =6 Hz, J₂ =10 Hz; C₃ --H), 3.36 (m; C₁ --H), 4.17 (q; OCH₂).

EXAMPLE 4 Ethyl 2-methyl-cis,endo-2-azabicyclo[3,3,0]octane-3-carboxylate 1.0 g of ethyl 1-methyl-1,4,5,6-tetrahydrocyclopenta[b]pyrrole-2-carboxylate (see Hauptmann et al., J. Prakt. Chem. 314, 353 (1972)) is dissolved in 50 ml of absolute alcohol and treated with 1.6 ml of concentrated sulfuric acid. 200 mg of rhodium-on-charcoal (5%) are added and the ixture is hydrogenated for 24 hours at 30° C. and under a hydrogen pressure of 10 bar. After the catalyst has been filtered off with suction, 8.3 g of saturated K₂ CO₃ solution are added; the solution is extracted with methylene chloride and the extract is dried over MgSO₄ and concentrated.

Yield: 1.0 g (97% of theory) of an oil which ispure (cis,endo configuration) according to ¹ H-NMR at 270 MHz.

¹ H-NMR (CDCl₃, 270 MHz): 1.26 (t, CH₃), 1.30-1.81 (m; 7H), 2.19-2.31 (m; C₄ --H overlapping with s 2.30, N--cH₃), 2.44-2.60 (m; 1H), 2.78 (dd, J₁ =6 Hz, J₂ =8 Hz; C₁ --H), 2.92 (dd, J₁ =6 Hz, J₂ =12 Hz; C₃ --H), 4.17 (q; OCH₂). 

What is claimed is:
 1. A compound of the formula ##STR12## in which n is 1, 2 or 3R¹ denotes hydroxyl or (C₁ -C₆)-alkoxy and R² denotes p-nitrobenzyl, p-methoxybenzyl, alpha-phenylethyl or benzhydryl.
 2. A method of using a compound as claimed in claim 1, wherein said compound is used in the preparation of an angiotensin-converting enzyme inhibitor.
 3. A compound as claimed in claim 1, wherein n=1. 